As to cost, why not ask Apple?
There are some folk that fret about such updates. But for the software ones I know I can skip it and move on. The hardware ones are tougher. Such as I won't get a Macbook air today as the update is very soon. I would get the other Macbooks since they are very current.
So I'm a long-time PC (read Windows) user who has had it! Finally decided to make "the switch". Now the only question is ... should I wait a couple of more months for Lion? Pros? Cons? If I buy my Mac now, will it be considered an "upgrade" to get Lion, or a full-blown OS purchase? How much is a typical upgrade? New OS purchase?